Interpretation ID: nht76-2.4

DATE: 02/25/76

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: General Motors Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in response to your letter of February 10, 1976, concerning the definition of "daylight opening" (DLO) as specified in Motor Vehicle Safety Standard No. 219, Windshield Zone Intrusion, 49 CFR 571.219, and concerning the procedure used by General Motors to determine DLO.

Your letter states that General Motors is concerned about the definition of DLO as stated in Standard No. 219, and "believes that the wording is not easily understood." The definition of DLO as stated in the Standard is based upon the definition found in paragraph 2.3.12 of Section E, Ground Vehicle Practice, SAE Areospace Automotive Drawing Standards, September, 1963. The SAE definition was slightly modified to reflect the particular characteristics of Standard No. 219. The last phrase of the SAE definition was changed to read "as measured parallel to the outer surface of the glazing material," because there was concern that there might be some confusion if the definition directed measurement by means of a "vertical projection".

Your letter describes General Motors' procedure for obtaining DLO, and asks if this procedure is consistent with the definition of DLO as specified in Standard No. 219. The answer to your question is yes. Your illustration (Figure 1) shows that you are measuring "parallel to the outer surface of the glazing material". Your Figure 1 is a simplified illustration, of course, since nearly all windshields are curved.

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